This letter demonstrates the effect of potassium (K) doping at the donor-acceptor interface of CuPc/ C60 -based organic solar cells. Power conversion efficient (PCE) doubled when a little K was doped into the CuPc/ C60 interface and the device was postannealed (75 °C, 10 min). Changes in binding energies, depletion capacitance, and mobilities of electrons and holes were investigated. The marked improvement of PCE arose mostly from the increase in short-circuit current, owing to the modified charge transfer process.
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